Hepatitis E virus (HEV) is the most recently characterized of five viruses known to produce the majority of cases of hepatitis worldwide. Limited studies suggest that a substantial proportion of cases of acute viral hepatitis in Asia, the Indian subcontinent, and Africa is due to HEV infection. At the time of the epidemic, virus-specific diagnostic tests were not available and the disease was thought to be due to a variant of HAV that overwhelmed host immunity. Subsequent testing of stored specimens demonstrated that these patients did not have acute HAV or acute HBV infection. This newly identified disease was called enterically transmitted non-A, non-B hepatitis and suggested the presence of at least one other hepatitis virus. Prior to production of HEV antigens by recombinant DNA technology, anti-HEV was detected by immune electron microscopy with stool-derived virus or by blocking fluorescent microscopy with antigen from the liver of infected macaques. Subsequently, recombinant expressed proteins and synthetic peptides, primarily from open reading frame (ORF) 2, have been used to develop immunoblotting assays and enzyme immunoassays for the detection of anti-HEV activity. Amplification of RNA by reverse transcription-PCR (RT-PCR) has been used to detect HEV RNA in the stools of experimentally infected animals, as well as in humans with hepatitis E. Early studies indicated that active immunization with recombinant ORF2 proteins provided some protection from infection in the cynomolgus macaque model.

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